Besides injection molding, the hot forming or thermoforming of thin thermoplastic films and plates, which are fixedly clamped at the edges, into three-dimensional molded articles, accompanied by thinning of the wall thicknesses thereof, constitutes the most important method in the macroscopic range for manufacturing large numbers of plastic articles. In contrast to injection molding, this method makes it possible to produce thin-walled, large-area, three-dimensional microstructured parts and microstructures in the microtechnical range.
Conductor tracks on three-dimensional injection-molded or hot-stamped plastic parts are mostly fabricated using MID technology (molded interconnect devices). Typical variants of this method include, for example, two-component injection molding, hot-stamping, mask-exposure methods, laser direct structuring and film insert molding. Known methods can be used to produce three-dimensional structures having integrated conductor tracks. Such methods do not, however, lend themselves to the fabrication of three-dimensional, membrane-type structures that are thin-walled on all sides, particularly not to those having undercuts.
When the existing MID method is employed, the problem arises that conductor tracks can only be introduced into three-dimensional structures at great outlay and/or at widths greater than 10 μm. This limits the design freedom, particularly when working with structures on the microscopic scale.
In this context, among the MID methods, two-component injection molding offers the greatest geometric freedom. However, depending on the flow properties and the flow lengths in the tool, the smallest feasible conductor track width is within a size range of about 250 μm. See Krautheim, T. B., Herstellungsverfahren, Gebrauchsanforderungen und Materialkennwerte Räumlicher Elektronischer Baugruppen 3-D MID [Production Methods, Usage Requirements and Material Parameters of Three-Dimensional Electronic Modules, 3-D MID]: Manual for Users and Manufacturers, Research Association for Three-Dimensional Electronic Modules, 2nd edition, 1999.
It may be that smaller conductor track geometries (of approximately 125 μm) are attainable using other methods, such as, for example, hot-stamping. However, they pose clear limitations on the design of the molded articles. In the case of laser structuring, geometries of up to approximately 30 μm are partially attainable (for example, using semi-additive methods). However, in this case, complex component geometries require substantial systems engineering work (multiaxis systems, 3D focal position control).
The disadvantage typically associated with resist-based laser structuring methods is that it is only possible to homogeneously coat three-dimensional components when working with comparatively simple geometries. This method is therefore only economical on a large scale in the area of fine conductor structuring. See Krautheim, cited above.
Mask-based methods for the laser structuring of conductor tracks either have the disadvantages typical of a mask projection, or they necessitate the fabrication of costly three-dimensional masks for the exposure process. Therefore, the contact masking method is also only suited for relatively simple component geometries and for relatively large components since, in the microscopic range, considerable additional outlay is still required for precise positioning. In the case of film insert molding, the three-dimensionality of the structures is limited due to the occurrence of folds during the shaping process.